Causation, Correlation, Aggression, and Political Rhetoric

John Sides at the Monkey Cage weighs in with some social science on the relationship between militant metaphors in political speech and individuals’ willingness to engage in actual political violence against government officials. The findings he cites: an experimental study has shown there seems to be no effect on the overall population of exposure to “fighting words” in political ads, but there is an effect on people with aggressive tendencies. Moreover:

This conditional relationship — between seeing violent ads and a predisposition to aggression — appears stronger among those under the age of 40 (vs. those older), men (vs. women), and Democrats (vs. Republicans).

But his real point is that we should be cautious of inferring from this or any wider probabilistic data causation regarding a specific event:

To prove that vitriol causes any particular act of violence, we cannot speak about “atmosphere.” We need to be able to demonstrate that vitriolic messages were actually heard and believed by the perpetrators of violence. That is a far harder thing to do. But absent such evidence, we are merely waving our hands at causation and preferring instead to treat the mere existence of vitriol and the mere existence of violence as implying some relationship between the two.

UPDATE: Two other points of view from political scientists: Henry Farrell and Dan Nexon.